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Props don't counter rotate?


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On 8/24/2021 at 11:58 AM, grafspee said:

There is additional torque at take off, created by prop inertia while engines accelerating to max rpm, you can minimize it by slowly adding power, but in flight when rpm is settled this torque is not present.

Torque doesn’t magically disappear. Nor does it vary due to propeller inertia. 

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9 minutes ago, =475FG= Dawger said:

Torque doesn’t magically disappear. Nor does it vary due to propeller inertia. 

Bad words, I was thinking about airframe reacting to rapid rpm increase, which you can mitigate by adding power at slower rate. Rapid throttle movement definitely are inducing harder to control roll tendency.

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One of the biggest issues with rapid throttle movement is the torque effects get ahead of the airflow over the tail. 
 

Airflow over the tail due to propwash is something very poirly modeled in DCS. In a real airplane you can blip the throttle to get some airflow to swing the tail during taxi. You cant do that in DCS. Also, early in the takeoff run, there is no airflow modeled, making the aircraft behave strangely. 
 

Luckily, torque is very milquetoast in DCS so it isn’t too much of an issue. 

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Counter rotating props are supposed to counter each others torque. Supposed to and actually do are 2 different things, by the way. That torque does have to go somewhere, and depending on which direction the torque is being applied, it will either be inboard or outboard of the roll axis and generally just places a lot of stress on that portion of the wing. In a perfect world they would cancel each other out, but it does effectively minimize the P effect enough to not be overbearing for the pilot; you can take the KA50 as a good example and see that the heli will spin regardless of the torque being cancelled out.  Now contra-rotating propellers DO. The torque is effectively placed squarely on the pylon of the working engine.


Edited by Hammer1-1

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5 hours ago, =475FG= Dawger said:

milquetoast

Well, I learned a new word today. 👨‍🎓

“Mosquitoes fly, but flies don’t Mosquito” :pilotfly:

- Geoffrey de Havilland.

 

... well, he could have said it!

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6 hours ago, =475FG= Dawger said:

One of the biggest issues with rapid throttle movement is the torque effects get ahead of the airflow over the tail. 
 

Airflow over the tail due to propwash is something very poirly modeled in DCS. In a real airplane you can blip the throttle to get some airflow to swing the tail during taxi. You cant do that in DCS. Also, early in the takeoff run, there is no airflow modeled, making the aircraft behave strangely. 
 

Luckily, torque is very milquetoast in DCS so it isn’t too much of an issue. 

I think you haven't done that, but prop wash is modeled, as you stand still if you apply power you can lift tail with your stick, as well control surfaces are reacting to prop wash, in P-51 trim system starts to work even at very low power setting.

Second thing in those planes you can't turn plane with rudder only, i particular searched for in cockpit recordings looking how pilots operate those warbirds they always use differential braking for turning, it is very obvious in case of spitfire, you can see and hear how often air brakes are used while taxing.

 

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52 minutes ago, grafspee said:

I think you haven't done that, but prop wash is modeled, as you stand still if you apply power you can lift tail with your stick, as well control surfaces are reacting to prop wash, in P-51 trim system starts to work even at very low power setting.

Second thing in those planes you can't turn plane with rudder only, i particular searched for in cockpit recordings looking how pilots operate those warbirds they always use differential braking for turning, it is very obvious in case of spitfire, you can see and hear how often air brakes are used while taxing.

 

Your above examples do not mean the airflow is correctly modeled.


And stating that you can’t turn a taildragger with the rudder only just after mentioning lifting the tail off the ground with the airflow from the prop points to something you might want to think about.

 

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7 minutes ago, =475FG= Dawger said:

Your above examples do not mean the airflow is correctly modeled.


And stating that you can’t turn a taildragger with the rudder only just after mentioning lifting the tail off the ground with the airflow from the prop points to something you might want to think about.

 

The power level which require to lift tail is quite big and it makes taxing impossible.

For example Bf-109 was known from poor rudder efficiency, if it was possible to do that what you saying, than at higher power pilot should not have any problem with keeping plane on runway, so using brakes would not be required. From small puff of air,  you cant expect that plane will drive like a car 😛

And i think Nick would notice that kind of miss modeling, what you are saying is not a small bug.


Edited by grafspee

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10 minutes ago, grafspee said:

The power level which require to lift tail is quite big and it makes taxing impossible.

For example Bf-109 was known from poor rudder efficiency, if it was possible to do that what you saying, than at higher power pilot should not have any problem with keeping plane on runway, so using brakes would not be required. From small puff of air,  you cant expect that plane will drive like a car 😛

And i think Nick would notice that kind of miss modeling, what you are saying is not a small bug.

 

 

 

If you can lift tail with power, a short burst of power against a deflected rudder will provide the airflow to move the tail laterally, especially when going with the torque ( left in the case of right hand engines). It certainly is enough airflow to stop the tail from moving laterally which is one of the primary uses of the technique of blipping the throttle, stopping a turn.


Your argument that a rudder effective enough to move the tail with a short burst of power at taxi speed would then be easily able to counter sustained maximum power is fallacious and not relevant. 

 

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1 hour ago, =475FG= Dawger said:

 

 

If you can lift tail with power, a short burst of power against a deflected rudder will provide the airflow to move the tail laterally, especially when going with the torque ( left in the case of right hand engines). It certainly is enough airflow to stop the tail from moving laterally which is one of the primary uses of the technique of blipping the throttle, stopping a turn.


Your argument that a rudder effective enough to move the tail with a short burst of power at taxi speed would then be easily able to counter sustained maximum power is fallacious and not relevant. 

 

No. For p51 you need almost 40 inch without brakes plane almost launch for take off. 

It is fallacious and not relevant, yeah because it is something completely disconnected 😛 It is very relevant both things apply to same principle airflow through tail section, why plane would react instantly to short burst of power and at the same time would not react at constant power and airflow ??

In planes where tail section is much larger compare to prop and engine that it would be possible, but warbirds usually have very small tail stab section.

I dont know any other sim which would simulate that, and most common sims available make me sick how taxing is modeled.


Edited by grafspee

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2 hours ago, grafspee said:

No. For p51 you need almost 40 inch without brakes plane almost launch for take off. 

It is fallacious and not relevant, yeah because it is something completely disconnected 😛 It is very relevant both things apply to same principle airflow through tail section, why plane would react instantly to short burst of power and at the same time would not react at constant power and airflow ??

In planes where tail section is much larger compare to prop and engine that it would be possible, but warbirds usually have very small tail stab section.

I dont know any other sim which would simulate that, and most common sims available make me sick how taxing is modeled.

 

I have done it in GodSim and it works as I described. 

 

Here is a good taildragger training film for further education.

 

 


Edited by =475FG= Dawger

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43 minutes ago, =475FG= Dawger said:

I have done it in GodSim and it works as I described. 

 

Here is a good taildragger training film for further education.

 

 

 

He said "use full rudder and apply brake to turn 🙂 

And no one would slam throttle in planes with big engines, so what you saying is even less likely after watching this training move. And this sharp turn, when he taxi out of parking slot, is obvious done with differential braking.


Edited by grafspee

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I'm loving this thread, guys. Learning so much!

 

another vote for the word of the day "milquetoast".  Funnily enough it's a French spelling of an English bland breakfast "milktoast". Yet we use the French spelling for some odd reason. This language is so backwards. 😄

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30 minutes ago, peachmonkey said:

I'm loving this thread, guys. Learning so much!

 

another vote for the word of the day "milquetoast".  Funnily enough it's a French spelling of an English bland breakfast "milktoast". Yet we use the French spelling for some odd reason. This language is so backwards. 😄

Milquetoast was a cartoon character created back in the 1920s, my limited knowledge of French is that milk is lait 😉

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2 hours ago, grafspee said:

He said "use full rudder and apply brake to turn 🙂 

And no one would slam throttle in planes with big engines, so what you saying is even less likely after watching this training move. And this sharp turn, when he taxi out of parking slot, is obvious done with differential braking.

 

More than once he states that brakes should only be used when absolutely necessary and that you should use moderate bursts of power to assist in moving the tail. In addition, why put in full rudder if rudder can’t turn the airplane?

 

And as I said, I have first hand knowledge of this technique. I am not making it up.

 

This is why any discussion of WWII flight modeling is so frustrating.  

7 minutes ago, Baldrick33 said:

Milquetoast was a cartoon character created back in the 1920s, my limited knowledge of French is that milk is lait 😉

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15 minutes ago, Baldrick33 said:

Milquetoast was a cartoon character created back in the 1920s, my limited knowledge of French is that milk is lait 😉

 

yes, you're spot on, however it's the French spelling of an English word "milk" and not a translation, that's what's funny about it. 😄 

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55 minutes ago, =475FG= Dawger said:

More than once he states that brakes should only be used when absolutely necessary and that you should use moderate bursts of power to assist in moving the tail. In addition, why put in full rudder if rudder can’t turn the airplane?

If you are saying that in DCS rudder deflection don't induce turn on the ground, then you are wrong. I can steer in small extent planes in DCS, for example keeping spitfire rolling straight rudder is only thing which you need, but for sharp turns or if i want to stop spin i will use brakes rudder alone won't help.

Listen to this and count how many times he used brakes. He used brakes to initiate sharp turn and he used brakes to stop this turn he didn't used any burst of power. This bi plane from training video is not a spitfire or bf-109, it may be steerable to higher extent but spit or bf-109 is difrent story.

 


Edited by grafspee

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3 hours ago, grafspee said:

If you are saying that in DCS rudder deflection don't induce turn on the ground, then you are wrong. I can steer in small extent planes in DCS, for example keeping spitfire rolling straight rudder is only thing which you need, but for sharp turns or if i want to stop spin i will use brakes rudder alone won't help.

Listen to this and count how many times he used brakes. He used brakes to initiate sharp turn and he used brakes to stop this turn he didn't used any burst of power. This bi plane from training video is not a spitfire or bf-109, it may be steerable to higher extent but spit or bf-109 is difrent story.

 

 

Initially, he is using the brakes to control his taxi speed. The sound you are hearing are the brakes releasing, not brake application. At 2:04, you hear the brake release. At 2:05 you can hear the engine rev up for his left turn to line up, and then you hear brakes again, likely opposite brake to control the left swing.

 

If you listen carefully to the prior training video, you will note that the instructor stated that one of the keys to taxying in an S turn is to begin stopping the turn almost the instant you begin the turn. This is one of the hardest skills for a new tail dragger pilot to learn, anticipating and leading the end of turns. In a real tail dragger, once you get the tail swinging, it doesn't want to stop and if you are late countering that, the back becomes the front very quickly.

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14 minutes ago, =475FG= Dawger said:

Initially, he is using the brakes to control his taxi speed. The sound you are hearing are the brakes releasing, not brake application. At 2:04, you hear the brake release. At 2:05 you can hear the engine rev up for his left turn to line up, and then you hear brakes again, likely opposite brake to control the left swing.

 

If you listen carefully to the prior training video, you will note that the instructor stated that one of the keys to taxying in an S turn is to begin stopping the turn almost the instant you begin the turn. This is one of the hardest skills for a new tail dragger pilot to learn, anticipating and leading the end of turns. In a real tail dragger, once you get the tail swinging, it doesn't want to stop and if you are late countering that, the back becomes the front very quickly.

Every brake release is after brake apply so, brake release = brake applied.

Second thing in spitfire,while you deflecting rudder and applies brake it will brake only one wheel or it will brake both but with different force so if you want or not you will use brakes to turn in spitfire 😛

I noticed that you referring to tail draggers why, so your assumption  is that every one act exactly the same ?


Edited by grafspee

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3 hours ago, grafspee said:

 

I noticed that you referring to tail draggers why, so your assumption  is that every one act exactly the same ?

 

A lot of experience, mostly. They all behave in generally similar ways with some variation due to engine/tail placement/design.

3 hours ago, grafspee said:

Every brake release is after brake apply so, brake release = brake applied.

Second thing in spitfire,while you deflecting rudder and applies brake it will brake only one wheel or it will brake both but with different force so if you want or not you will use brakes to turn in spitfire 😛

 

 

The key is to watch the sequence of events. Brake release, power application and then another brake release tells me he released the brakes to turn left, bumped the throttle to start the tail swinging right with left rudder applied and then applied full right rudder and then applied brake to check the tail swing so that he arrived smoothly lined up and not going in circles.

 

 

 

 

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8 hours ago, =475FG= Dawger said:

A lot of experience, mostly. They all behave in generally similar ways with some variation due to engine/tail placement/design.

The key is to watch the sequence of events. Brake release, power application and then another brake release tells me he released the brakes to turn left, bumped the throttle to start the tail swinging right with left rudder applied and then applied full right rudder and then applied brake to check the tail swing so that he arrived smoothly lined up and not going in circles.

 

For me it look like he added throttle to keep rolling faster, i can see that he braked quite hard to enter this turn and i can see that plane start turning before he added throttle.

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I figured out early on you need to add power to turn the tail. Hold the brakes, add enough power to get some rudder authority, put some rudder in and the plane will turn. Its about the only way you can taxi the spit. Obviously all tail draggers behave the same; the only thing that separates most other aircraft is whether or not it has differential brakes so otherwise you would be using your toe brakes to induce a turn.


Edited by Hammer1-1

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40 minutes ago, Hammer1-1 said:

I figured out early on you need to add power to turn the tail. Hold the brakes, add enough power to get some rudder authority, put some rudder in and the plane will turn. Its about the only way you can taxi the spit. Obviously all tail draggers behave the same; the only thing that separates most other aircraft is whether or not it has differential brakes so otherwise you would be using your toe brakes to induce a turn.

 

You can taxi spitfire using brakes too.

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3 hours ago, =475FG= Dawger said:

In this video you can clearly hear power added to make the turn at 16:45

 

He also added power for the initial right turn out of the parking pad.

 

 

But the reason to add power could also be that he doesn't want to come to a stop because he knows that he'll use the brake for the turn while taxiing on grass.

 

If you fly a (coordinated)turn you also anticipate the additional power necessary to stay at your altitude and speed while performing the turn, right? And just before leveling off you reduce the power, to prevent acceleration. 

 

He also kept some power while taxiing at some positions. It is hard to tell the reasons for a resulting action without knowing the intention and actions of the pilot and other factors like friction changes of the underground. 

 

There could also be a slight slope that would cause the P-51 to come to a stop while taxiing so slowly and turn without additional thrust. Just not visible enough on a GoPro fisheye. 

 

I could make a video with opposite ruder use while using the brake to turn and not showing my toebrakes. Without knowing my intentions and actions one could come to the conclusion that right rudder input causes a left turn.

This would work with a P-51 of Bf109, etc. but never with a Spitfire. There you have to use the rudder for differential braking. If the rudder was the main means for turning, then you should turn sufficiently without the brake(as you should use it only when necessary), and stop the turn, but we can can hear the constant use of the brake and its "pffff" in the previous video. 

You can't turn a Spitfire without using the pedals, because the rudder and wheelbrakes are mechanically connected to the pedals, so it is hard to tell from a video what is the primary reason(rudder or brake) of the force that causes the aircraft to turn.

 

So to come to the conclusion(of Kermit's video) that he added power to turn with the rudder is not necessarily the correct conclusion. It is a possibilty, but with enough uncertainties to not use it as a proof of your claim("he added power for the rudder to turn").

 

 

34 minutes ago, Hammer1-1 said:

Hold the brakes, add enough power to get some rudder authority, put some rudder in and the plane will turn.

This way you automatically apply differential braking unless you completely release the brake lever.

Can you taxy and turn without ever touching the brake lever?

 

Fox

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